Upgrade slack_sdk to 3.1.1

Author: seratch

setup.py

@@ -33,7 +33,7 @@
         exclude=["examples", "integration_tests", "tests", "tests.*",]
     ),
     include_package_data=True,  # MANIFEST.in
-    install_requires=["slack_sdk>=3.1.0,<3.2",],
+    install_requires=["slack_sdk>=3.1.1,<3.2",],
     setup_requires=["pytest-runner==5.2"],
     tests_require=test_dependencies,
     test_suite="tests",